Apparatus for electrostatic precipitation of dust



y 20, 1969 SENICHI MASUDA 3,444,668

APPARATUS FOR ELECTROSTATIC PRECIPITATION 0F DUST Filed larch e, 19 4 V Sheet I of a y 1969 SENICHI MASUDA 3,444,668

APPARATUS FOR ELECTROSTATIC PRECIPITATION OF DUST Filed March a, 1964 Sheet 3 of s May 20, 1969 SENICHI MAsuDA 3,

APPARATUS FOR ELECTROSTATIC PRECIPITATION OF DUST Filed March 6, 1964 Sheet 3 or a United States Patent 3,444,668 APPARATUS FOR ELECTROSTATIC PRECIPITATION 0F DUST Senichi Masuda, Tokyo, Japan, assignor to Onoda Cement Company, Limited, ()noda, Yamaguchi, Japan Filed Mar. 6, 1964, Ser. No. 349,997

Int. Cl. B03c 3/78, 3/01 US. Cl. 55-118 3 Claims This invention relates to an apparatus for the electrical precipitation of dust in a dust-containing gas. More particularly, this invention relates to an apparatus comprising a device for drying water slurry of dust, at least one of dry system dust-precipitation chambers provided with discharge electrodes and collecting electrodes, at least one of the wet system dust-precipitating chambers is provided with water spraying nozzles, discharge electrodes and collecting electrodes, and the means for receiving and transporting water slurry of dust and also to a method for the electrical precipitation of dust by using the apparatus.

There have already been made various electrical dustprecipitators. However, the capabilities of these known electrical dust-precipitators are limited by their defects causing the redispersion of dust precipitated on the collecting electrodes and the corona discharge between the both electrodes due to the electric high resistance of dust in the dust-containing gas. These defects can not substantially be overcome unless the precipitated dust is washed ed with water by using a so-called wet system electrical dust-precipitator. Still, the capability of such a wet system dust-precipitator is limited in use due to the difficulty in disposing of water slurry produced from said dust-precipitator in which a large amount of Water is used.

The inventor has developed this invention in order to overcome the defects inherent in the prior art.

An object of this invention is to provide an improved and a high efficiency apparatus suitable for electrical precipitation of dust in a dust-containing gas with ease for disposing of water slurry.

Other objects of this invention will be obvious from the detailed explanation hereinafter.

In general, the apparatus of this invention is composed of a drying device, at least one Wet system dust-precipitating chamber, at least one dry system dust-precipitating chamber and means for receiving and transporting water slurry of dust. The Wet system dust-precipitating chamher is provided with a plurality of water spraying nozzles, dust-collecting electrodes and discharge electrodes. The dust precipitated on the collecting electrodes is washed ofi" with water sprays injected from the nozzles and the resulting Water slurry is transported to a device for receiving it. The dry system dust-precipitating chamber is provided With dust-collecting electrodes and discharge electrodes. The drying device is established on the front of the dry system dust-precipitating chamber and a dust-containing hot gas is successively passed through the drying device, the dry and wet system dust-precipitating chambers. The water slurry is charged immediately, or after thickened or filtered, into the drying device and dried by the heat of the dust-containing hot gas. Therefore, the apparatus of this invention has the capability of the wet system electrical dust-precipitatorse but has no handicaps as inherent in them. The drying device used in this invention is made in various types, for example, a spray dryer, a rotary dryer, a through-circulation dryer and the like. The means for receiving and transporting the water slurry include a hopper, a filter, a pump and a connecting pipe. A thickening device for the water slurry includes a centrifugal separator, a rotary dis filter and the like.

The apparatus of this invention may be similarly constrncted with the exception that all the dry system dustprecipitating chambers are substituted by the wet system dust-precipitating chambers. But it is more economical to provide one or more wet system dust-precipitating chambers on the outlet side of the dust-containg hot gas. This can be understood from the following explanation. Assume that the apparatus includes the first and the second dry system dust-precipitating chambers and the third wet system dust-precipitating chamber arranged along the flow direction of the dust-containing gas. In such an apparatus the substantial part of the dust is precipitated in the first and the second chambers and the remaining part of the dust can be completely precipitated in the third chamber by using a small amount of water. Therefore, the amount of Water slurry can be reduced by using the apparatus and the method of this invention. Further, all the dust flying in the drying device can be precipitated in the dust-precipitating chambers and also the dust-containing hot gas is humidified With the water vapour derived from the evaporation of the Water slurry to be charged into the drying device. As a result, the dry system dust-precipitating chambers can be operated with a high efiiciency as the electric resistance of the dust is decreased and a corona discharge between electrodes does not occur. In addition, when the high humidity dust-containing hot gas is rapidly cooled in the wet system dustprecipitating chambers, the dust in the gas is converted into large mist particles having a size of about 200 so in this case, the wet system dust-precipitating chambers can not be operated with high efliciency. As mentioned above, the apparatus of this invention has remarkable advantages.

When the water slurry produced from the wet system chambers is immediately sprayed into the drying device, the amount of water may be limited depending upon the amount of dust-containing gas to be charged, the number of dust-precipitating chambers and the particle size of the mist to be sprayed. In such a case, in general, it is preferable to use water in an amount of from 1 to 5 tons per hour per electrode on which the dust is precipitated. This is also true of the case when the water slurry is thickened by a centrifugal separator or filtered by a rotary disc filter to form it in cakes because the use of water in great excess requires a large capacity device for treating a large amount of water slurry.

It has been found from the inventors investigations that in the case of spraying the Water slurry into the drying device, it is preferable to use water slurry containing a solid substance in an amount of 5 to 30% by Weight and to use water mist having a size of 10 to 1000;1.. And also, it has been found that it is preferable to use filter cakes containing a solid substance in an amount of 70 to by weight in the case of drying the cakes in the drying device. Still further, it has been found that it is preferable to use the Water slurry containing a solid substance in an amount of more than the solid substance contained in the water slurry to be sprayed but less than the solid substance contained in the cakes in the case of drying the Water slurry in the rotary dryer or the chain grate dryer and also that it is preferable to use a dust-containing gas having a humidity between the dew point at a given tempeatnre and the moisture content at which a corona discharge does not occur, that is, having the humidity corresponding to 12 grams of Water per cubic meter of gas at normal atmospheric pressure and room temperature.

For a better understanding of the nature and objects as described above of this invention, reference should be had to the detailed explanation and examples hereinafter given in combination With the accompanying drawings in which:

FIGURE 1 is a vertical sectional view of an apparatus in accordance with this invention;

FIGURE 2 is a vertical sectional view of another apparatus in accordance with this invention; and

FIGURE 3 is a perspective view of a dust-precipitating chamber with a part broken away and in cross section.

Referring to FIGURE 1, the apparatus is provided with a drying tower 1, a first dry system dust-precipitating chamber 2, a second dry system dust-precipitating chamber 3, and a wet system dust-precipitating chamber 4 which are arranged in series along a flow direction or path of the dust-containing gas. The drying tower is provided with an inlet 5 for the dust-containing gas on top, a nozzle 6 for spraying water slurry at the upper part and an outlet 7 for the dust-containing gas at the lower side. The first and the second dust-precipitating chambers are provided with a dust-collecting electrode 8 as an anode and a discharge electrode 9 as a cathode respectively. The wet system dust-precipitating chamber is provided with a dust-collecting electrode 8 as an anode, a discharge electrode 9 as a cathode and a plurality of nozzles 10 for spraying water. The nozzle 6 placed at the upper part in the drying tower 1 is connected to a pipe 11 for supplying air or steam. The drying tower 1 is provided with a hopper 12 for receiving the dust at the bottom which is in communication with a screw conveyor 13. Also, the first and the second dust-collecting chambers are each provided with a hopper 14 and 15 for receiving the dust at the bottom which are in communication with the screw conveyor 13. The wet system dust-precipitating chamber 4 is provided with a hopper 1 6 for receiving the water slurry produced in said chamber. The hopper 16 is connected to a tank 18, for storing the water slurry, by a pipe 17. The water slurry stored in the tank 18 is transported to the nozzle 6 placed in the drying tower 1 through a pipe 19, a centrifugal separator 20, a pipe 21, a pump 22 and a pipe 23. The drying tower 1 is provided with a hammer 24 for preventing the accumulation of dust on the inner surface thereof and a hammer 25 for preventing the accumulation of dust on the outer surface of the nozzle 6. The spent water derived from the centrifugal separator 20 is transported to a tank 27 through a pipe 26. In the tank 27, the spent water is mixed with fresh water supplied by a pipe 2-8 from the water source (not shown). Then, the water is transported to the nozzle 10 arranged in the wet system dust-precipitating chamber 4 through a pump 29 and a pipe 30, and recycled for Washing the dust precipitated on the dust-collecting electrode 8. A stack 31 is provided at the end of the wet system dust-precipitating chamber 4 and the exhausted gas is removed from the stack. It must be understood that the dust-collecting electrode 8 may be an anode plate and is made of iron, steel, reinforced concrete slab, asbestos, acid resistant material or a material covered with the acid resistant material and that the discharge electrode 9 may be a cathode wire and is made of piano Wire or stainless steel wire. Also, the discharge electrode 9 is provided with the weight W at the bottom in order to prevent its vibration and its contact with the dust-collecting electrode.

EXAMPLE 1 .An apparatus as shown in FIG. 1 was evaluated by using a flue gas derived from a dry system rotary cement kiln. The apparatus was provided with a Wet system dustprecipitating chamber 4 possessing eighteen members of the dust-callecting electrode. The flue gas which contained the dust in the degree of 19 g./m. was charged into the drying tower 1 at the inlet 5 in the rate of 189,000 m. /hour at a temperature of 200 C. 24 tons of water per hour were sprayed from the nozzles 10 in the wet system dust-precipitating chamber 4 and about one ton of water was evaporated. Water slurry having a concentration of 0.75% was produced in an amount of 23 tons per hour. The water slurry was thickened to one-eighth by the centrifugal separator 20. The thickened water slurry was sprayed from the nozzle 6 of the drying tower 1 into said tower in the state of mist having a particle size of 50a in diameter. The drying operation was completed in the time of about 0.7 second. In this case, the charged flue gas was moistened with about 2.82 tons of steam vapour per hour which was derived from the mist of the water slurry and hence it was observed that the corona discharge did not occur in the first and the second dry system dust-precipitating chambers 2 and 3. And also, it was observed that the electric current density could be increased from 0.02 milliampere per square meter of the dust-collecting electrode 8 to 0.4 milliampere per square meter of said electrode and that the dust was recovered with a yield of about 95% in the first and the second chambers 2 and 3, and with a yield of about 5% in the Wet system dust-precipitating chamber 4. This proves the fact that substantially all the dust was recovered from the flue gas charged in the apparatus.

Referring to FIG. 2 it shows a modification of the appartus as shown in FIG. 1, which is provided with a drying device 1, the first dry system dust-precipitating chamber 2, the second dry system dust-precipitating chamber 3, a wet system dust-precipitating chamber 4, a flue gas inlet 5, an outlet 7, a dust-collecting electrode 8, a discharge electrode 9, a plurality of nozzles 10, a screw conveyer 13, a hopper 14, a hopper 15, a hopper 16, a pipe 17, a tank 18, a pipe 19, a pump 22, a pipe 23, a pipe 26, a tank 27, a pipe 28, pump 29, a pipe 30 and a stack 31, which are the same devices as in FIG. 1 and are operated in the same manner as in the apparatus shown in FIG. 1. In this modified apparatus, an agitation device constituting a plurality of blades 32 and a rotary axis 33 is provided in the drying device 1 and the dried mass in charged into the first dust-precipitating chamber 2 through the outlet 7. The water slurry stored in the tank 18 is transported to a disc filter 20 through the pipe 19, the pump 22 and the pipe 23. The water slurry is filtered in the disc filter 20 to separate water from and filter cakes are formed. The filter cakes are charged through a chute 34 and an inlet 6 into the drying device 1. A spent water derived from the disc filter 20 is transported to the tank 27 through a pipe 35, a pump 36 and the pipe 26. In the tank 27, the spent water is mixed with a fresh water supplied by the pipe 28 from the water source (not shown). Then, the water is transported to the nozzles 10 arranged in the wet system dust-precipitating chamber 4 through the pump 29 and the pipe 30, and recycled 'for washing the dust precipitated on the dust-collecting electrode 8. The stack 31 is provided at the end of the wet system dust-precipitating chamber 4 and the exhausted gas is removed from the stack.

EXAMPLE 2 An apparatus as shown in FIG. 2 was evaluated by using the same flue gas derived from a dry system rotary cement kiln as in Example 1 in the same manner as in Example 1. When 24 tons of water per hour were sprayed from the nozzle 10 in the wet system dust-precipitating chamber 4, the water slurry was received in the hopper 16 in an amount of 23 tons per hour. The water slurry was filtered by the disc filter 20 and formed into the cakes containing solid substance of by weight in an amount of 3 tons per hour. The filter cakes were charged into the drying device 1 and the operation is repeated in the same manner as in Example 1. It was observed that the corona discharge did not occur and that the dust was recovered with the same yield as in Example 1.

In the apparatus in accordance with this invention, there may occasionally be some trouble in that the pipings, the nozzles and the filter are clogged with calcium carbonate which results from the reaction of calcium hydroxide and carbon dioxide contained in the flue gas with the water supplied. But such incidents can be eliminated by introducing carbon dioxide or a part of the flue gas into the water slurry in the hopper 16 and the tank 18 to convert calcium hydroxide to calcium carbonate:

What I claim is:

1. Apparatus for separating and precipitating dust particles from a gas flow containing dust particles comprising, means defining a first chamber in which said gas flow is received, means for collecting and removing dust particles from said gas flow in said first chamber, means for mixing with said gas flow solid particles comprising a slurry of water and dust particles to remove dust from said gas flow in said first chamber, means defining a dry second chamber in communication with said first chamber, electrically energized electrodes in said second chamber for precipitating dust from said gas fiow received from said first chamber, means collecting and removing dust precipitated in said second chamber, means defining a third chamber in communication with said second chamber, receiving said gas fiow from said second chamber, electrically energized electrodes in said third chamber for precipitating dust particles from said gas flow in said third chamber, means for spraying water into said third chamber into contact with said gas and including spraying said electrodes for washing dust thereofi, collecting means collecting water and dust from said third chamber as a slurry, means connected to the last mentioned collecting means to apply said slurry to said gas flow in said first chamber, and means to remove water from said slurry before applying said slurry to said gas flow comprising a disc filter connected to said collecting means receiving a slurry from said collecting means to produce filter cakes and removing the water from said slurry for spraying into said third chamber, means for discharging the filter cakes and water as a slurry into said first chamber, and an agitator in said first chamber agitating the charged cakes in said first chamber for contacting the slurry with the gas flow containing dust particles.

2. Apparatus according to claim 1, including nozzle means for applying said slurry as a spray in said first chamber.

3. Apparatus according to claim 2, in which said first chamber is substantially vertically disposed, means introducing said gas flow into an upper part of said chamber for flow downwardly therein, and said nozzle means being disposed in said upper part discharging said slurry generally downwardly.

References Cited UNITED STATES PATENTS 1,766,422 6/1930 Wintermute et al. -136 1,932,467 10/1933 Keenan.

2,677,439 5/1954 Hedberg 55-124 3,212,235 10/ 1965 Markant.

HARRY B. THORNTON, Primary Examiner.

B. NOZICK, Assistant Examiner.

US. Cl. X.R. 

1. APPARATUS FOR SEPARATING AND PRECIPITATING DUST PARTICLES FROM A GAS FLOW CONTAINING DUST PARTICLES COMPRISING, MEANS DEFINING A FIRST CHAMBER IN WHICH SAID GAS FLOW IS RECEIVED, MEANS FOR COLLECTING AND REMOVING DUST PARTICLES FROM SAID GAS FLOW IN SAID FIRST CHAMBER, MEANS FOR MIXING WITH SAID GAS FLOW SOLID PARTICLES COMPRISING A SLURRY OF WATER AND DUST PARTICLES TO REMOVE DUST FROM SAID GAS FLOW IN SAID FIRST CHAMBER, MEANS DEFINING A DRY SECOND CHAMBER IN COMMUNICATION WITH SAID FIRST CHAMBER, ELECTRICALLY ENERGIZED ELECTRODES IN SAID SECOND CHAMBER FOR PRECIPITATING DUST FROM SAID GAS FLOW RECEIVED FROM SAID FIRST CHAMBER, MEANS COLLECTING AND REMOVING DUST PRECIPITATED IN SAID SECOND CHAMBER, MEANS DEFINING A THIRD CHAMBER IN COMMUNICATION WITH SAID SECOND CHAMBER, RECEIVING SAID GAS FLOW FROM SAID SECOND CHAMBER, ELECTRICALLY ENERGIZED ELECTRODES IN SAID THIRD CHAMBER FOR PRECIPITATING DUST PARTICLES FROM SAID GAS FLOW IN SAID THIRD CHAMBER, MEANS FOR SPRAYING WATER INTO SAID THIRD CHAMBER INTO CONTACT WITH SAID GAS AND INCLUDING SPRAYING SAID ELECTRODES FOR WASHING DUST THEREOFF, COLLECTING MEANS COLLECTING WATER AND DUST FROM SAID THIRD CHAMBER AS A SLURRY, MEANS CONNECTED TO THE LAST MENTIONED COLLECTING MEANS TO APPLY SAID SLURRY TO SAID GAS FLOW IN SAID FIRST CHAMBER, AND MEANS TO REMOVE WATER FROM SAID SLURRY BEFORE APPLYING SAID SLURRY TO SAID GAS FLOW COMPRISING A DISC FILTER CONNECTED TO SAID COLLECTING MEANS RECEIVING A SLURRY SAID COLLECTING MEANS TO PRODUCE FILTER CAKES AND REMOVING THE WATER FROM SAID SLURRY FOR SPRAYING INTO SAID THIRD CHAMBER, MEANS FOR DISCHARGING THE FILTER CAKES AND WATER AS A SLURRY INTO SAID FIRST CHAMBER, AND AN AGITATOR IN SAID FIRST CHAMBER AGITATING THE CHARGED CAKES IN SAID FIRST CHAMBER FOR CONTACTING THE SLURRY WITH THE GAS FLOW CONTAINING DUST PARTICLES. 